These studies will attempt to gain an increased understanding of the mechanisms of actions and interactions of neurotransmitters and neuromodulators within the tuberal hypothalamus. The techniques to be utilized in these studies are primarily electrophysiological. The activity of single neurons will be recorded with conventional extracellular glass microelectrodes and agents to be tested will be applied, either locally onto the cell surface by pressure or microiontophoresis or more generally by adding them to the perfusion fluid.. Major questions to be addressed concern the pharmacological types of receptors which are involved in mediating the effects of histamine on hypothalamic neurons, and whether these receptors are located pre- or post-junctionally. In addition, we will investigate the mechanisms by which gonadal steroids induce both short- and long-term changes in neuronal activity and whether these changes can be attributed to modulation of the actions of putative neurotransmitters by steroids.